The present invention relates to a device for separating an imbricated formation of printing products such as periodicals, brochures and the like which are continuously conveyed in a partially overlapping, imbricated manner, into a succession of spaced printing products.
In the manufacture of adhesive-bound printing products (brochures) it is necessary to dry these printing products between the adhesive binder and the following processing station, e.g. the three-side trimmer. This generally takes place using a relatively long conveyor track to which the printing products are transferred after the adhesive binder. To achieve short feed distances and low feed velocities the printing products are conveyed on the drying track in a continuous, imbricated formation in which the printing products overlie one another in an imbricated manner through partial overlapping. At the end of the drying track the imbricated formation must be separated into individually-conveyed printing products in order to be fed to the following processing station.
Separating devices are known which comprise a first conveyor driven at the velocity of the drying track and forming in a sense the end of the drying track, a second conveyor arranged after the first and driven at a second velocity which is higher in relation to the velocity of the first conveyor, and a de-imbricating device consisting of two pressure rollers for accelerating the leading printing product of the imbricated formation to the second velocity and for maintaining the imbricated arrangement of the following printing products being conveyed in the imbricated formation at the first velocity, the first pressure roller being arranged at the end of the first conveyor and the second pressure roller acting on the printing products at the start of the second conveyor. The effectiveness of the separating device depends on a large number of parameters which must be mutually adjusted. The parameters determined by the printing products are, for example, their size, which is defined by a width, a height and a thickness, their surface quality and their weight. Changeable parameters are, for example, the feed velocities, which determine the degree of imbrication as a measure of the mutual overlap of the printing products and the distance between the conveyed printing products after separation, the surface quality of the conveyor belts and of the pressure rollers, the position of the pressure rollers on the conveyors, and their application pressure, geometrical form and size, among other parameters.
The separation of flat printing products only a few millimetres thick and with low adhesion between their surfaces generally does not present a problem. With thicknesses of 4 mm and above, however, more complex adjustments are required. The reason is that the forces exerted by the pressure rollers are transmitted to the printing products as downwardly-widening cones of force, which are generated in particular by the increased inherent stiffness of the printing products along the bound side and are increased by mutually adhering surfaces. As a result, the leading printing product in the imbricated formation is still being held on the first conveyor while the second pressure roller is acting on this printing product to accelerate same. This gives rise to undefined removal processes which manifest themselves in skewed positioning and uneven spacing of the individually conveyed printing products. Simultaneous removal or entrainment of two or more printing products may also occur which are then transported further while retaining their imbricated arrangement. In the case of relatively thick printing products the first pressure roller literally jumps over the upwardly projecting edges of the imbricated formation, giving rise to irregular, practically oscillating pressure relationships. Although this can be countered by increasing the pressure of the rollers, the printing products are thereby deformed to become a dished, imbricated formation which is therefore difficult to separate.